This invention relates to an ink cartridge which encompasses at least one ink container which has an ink outlet with an ink outlet opening which extends from the inside to the outside, in the ink outlet opening a differential pressure valve is mounted which comprises a valve seat and a valve body which can move relative to it, the valve seat has a continuous valve opening which has a peripheral sealing surface outside, a spring means is attached between the movable valve body and the stationary ink outlet, the valve body is pressed by the spring means with a predetermined closing force to form a seal from the outside against the sealing surface of the valve seat, and can be moved against the closing force to the outside from the sealing surface.
Ink cartridges of the indicated type are used as interchangeable ink tanks for ink supply of inkjet printing devices. Generally they have a housing which is made for attachment in the corresponding receiver of a printer. In the housing of the ink cartridge one or more ink containers which can be filled with different inks are made as the actual ink reservoirs. Each ink container has an ink outlet opening for detachable connection to the ink supply connection of the printer. In this way ink is supplied to the printer in operation. When the ink contained in the ink container has been used up, the empty ink cartridge can be easily taken out of the receiver and can be replaced by a full ink cartridge. The empty ink cartridges are either thrown away or refilled with ink for re-use.
Smaller inkjet printers of simple structure require that the ink at the ink outlet of the ink cartridge be at a given negative pressure level which corresponds to the negative pressure which is produced by the print head during operation at the ink supply connection of the printer. The negative pressure level must be kept within narrow limits: On the one hand, it must be ensured that the ink does not run out of the ink cartridge by itself due to the force of gravity and disrupt the operation of the print head, on the other hand the pressure level may not be so high that ink can no longer be sucked out by the print head.
In order to keep the ink ready at the ink outlet opening of the ink cartridge at a predefined negative pressure, placing a differential pressure valve in the ink outlet is known. It opens when the print head is working and is intaking the ink, by which a negative pressure is produced on the ink supply connection, and ink can flow to the print head.
Ink cartridges with differential pressure valves in the ink outlet are known in diverse versions, for example from EP 238 829 B1. It describes a valve with a cap-shaped valve body which spring-loaded seals against the sealing surface of the ink outlet opening from the outside and clears the passage opening when a predetermined negative pressure level on the outside of the differential pressure valve is not reached by the print head. The use of an elastic valve body does have the advantage of a simple structure. But the disadvantage is that production of an elastic valve body with the required precision of elastic properties in large numbers is relatively complex. Moreover the properties of elastic materials change with time, so that the valve becomes leaky or the pressure difference which is required for opening becomes too high or too low.
To some extent, the aforementioned problems can also be resolved by the valve body being pressed by a spring element against a valve seat. This concept is described for example in EP 709 207 B1. The version of the valve known from it has the major disadvantage that even slight misorientation of the valve body relative to the sealing surface leads to operating problems. But this is the normal case since the valve body can move in the ink outlet opening and for this reason necessarily has mechanical play. In this way the differential pressure valve in the closed state can be leaky, by which the negative pressure level at the ink outlet cannot be maintained, consequently ink emerges uncontrolled and malfunctions and damage on the printer can occur.
In view of the aforementioned problems in the existing art, it is an object of the invention to devise an ink cartridge with a differential pressure valve which works more reliably.